This application is related to and claims priority from Japanese Patent Application No. 00-050452, filed on Feb. 22, 2000.
The present invention generally relates to the field of optical modules and more particularly to an optical module with an optical waveguide formed using a resin containing fluorine.
Recent years have seen active research and development of optical modules that use polymer-based optical waveguides, which provide lower costs compared to quartz-based optical waveguides. Of these, optical waveguides that use polyamides as the polymer material have good heat resistance and reliability, providing advantages in terms of process applicability and practicality. Furthermore, the use of fluorine reduces Cxe2x80x94H bonding, allowing optical transmission loss to be reduced. Examples of this conventional technology include Japanese laid-open patent publication number Hei 9-21920, Japanese laid-open patent publication number Hei 10-288717, Japanese laid-open patent publication number Hei 11-133254.
In order to reduce transmission loss in the 1.3-1.6 micro-meter wavelengths used in optical communications, fluorine is introduced in these polymer-based optical waveguides to reduce the Cxe2x80x94H bonding, which causes this transmission loss. Standard optical waveguides are formed, starting from the lowest layer, from a lower cladding layer, a core layer, and an upper cladding layer. Fluorine is used not only in the core layer but also in the upper and lower cladding layer. This is because some light leaks out from the core layer to the cladding layer, thus making loss in the cladding layer an issue.
Silicone-based resins are often used as the adhesives and encapsulants used in optical modules since they can limit stress with low elasticity and also since water absorption is low. In these cases, the surface of the optical waveguide substrate, the optical elements, and the like of the optical module are cleaned before the silicone-based resin in applied, thus improving the reliability of the adhesion between these elements and the silicone-based resin. This ensures that the module will operate in a reliable and stable manner.
Cleaning is performed, for example, by exposing the optical module to ultraviolet light or by performing plasma ashing. Alternatively, the optical waveguide and the optical fibers can be connected using an ultraviolet-setting adhesive. In these cases as well, the surface of the optical waveguide is exposed to ultraviolet light to set the ultraviolet-setting adhesive.
According to our research, if the upper cladding layer material is formed from a resin containing at least 10% of fluorine by weight, this surface is exposed to ultraviolet light or to plasma ashing, silicone-based resin is applied to the surface and set, then there is inhibition to the setting of the silicone-based resin. More specifically, if the upper cladding layer material contains at least 10% fluorine, putting a needle to the silicone-based resin and then moving it away after the silicone-based resin is set will cause filaments to be drawn. It was also found that actions such as the tilting optical module will cause the silicone-based resin to flow.
Thus, there is a need to provide an optical module that can limit inhibitions to the setting of silicone-based resin.
The present invention provides an optical module and apparatus and forming method that can reduce problems in the setting of a silicone-based resin. In one embodiment of the present invention an optical module is provided. The optical module includes: an optical waveguide formed from a first resin, the first resin having fluorine; an intermediary layer above the optical waveguide; and a silicone-based resin layer above the intermediary layer. The intermediary layer may include: a metal, a dielectric, an inorganic compound, or a second resin having a fluorine content of less than 10 percent.
Another embodiment of the present invention includes an intermediate layer interposed between an upper cladding layer and a silicone-based resin. The intermediate layer is formed, for example, from at least one item selected from the following list: a metallic or non-metallic inorganic layer; a resin layer not containing fluorine; and a resin layer with a low fluorine content.
In one embodiment of the present invention a method for producing an optical module is provided. The method includes: forming an optical waveguide having a resin, the resin having fluorine. Next, forming above said optical waveguide, an intermediate layer; and lastly, forming a covering layer above the intermediate layer, the covering layer having a silicone-based resin. The intermediate layer is selected from a group including a metal, a dielectric, an inorganic compound, a second resin having a fluorine content of less than 10 percent or any combination thereof.
More specifically, for example, an optical module includes an optical waveguide formed from a resin containing at least some fluorine. A silicone-based resin is present in at least part of an upper section of the optical waveguide. A metal film is interposed between the optical waveguide and the silicone-based resin.
According to another embodiment of the present invention, the metal film is formed from at least one type of metal selected from the group of: Al, Ti, Ta, Cr, Mo, W, Mn, Fe, Ni, Cu, Pt, and Au.
According to another embodiment of the present invention, an optical module includes an optical waveguide formed from a resin containing at least some fluorine. A silicone-based resin is present in at least part of an upper section of the optical waveguide. An inorganic film is interposed between the optical waveguide and the silicone-based resin.
The inorganic film is formed from at least one material selected from the group of: Si, SiO2, Si3N4, Ta2O5, and Al2O3.
According to another embodiment of the present invention, an optical module includes an optical waveguide formed from a resin containing at least some fluorine. A silicone-based resin is present in at least part of an upper section of the optical waveguide. A resin layer not containing fluorine is interposed between the optical waveguide and the silicone-based resin.
According to another embodiment of the present invention, an optical module includes an optical waveguide formed from a resin containing at least some fluorine. A silicone-based resin is present in at least part of an upper section of the optical waveguide. A resin layer with a fluorine content of no more than 5% total weight is interposed between the optical waveguide and the silicone-based resin.
According to another embodiment of the present invention, the resin containing at least some fluorine is a polyamide.
According to another embodiment of the present invention, the resin layer containing no fluorine is a polyamide formed from a repeating unit represented by the chemical formula below (Chemical Formula 1).
(In the formula, R1 is at least one of the tetravalent organic groups selected from the set shown below (Chemical Formula 2), and R2 is at least one of the divalent organic groups selected from the set shown below (Chemical Formula 3).) 
It is believed that hardening is obstructed in the conventional technology because when ultraviolet exposure or plasma ashing is applied on material containing fluorine, some of the groups with which fluorine is associated are exposed at the surface in an activated state. This results in interaction with the setting catalysts in the silicone-based resin, making it more difficult for the silicone-based resin to harden. Alternatively, it may be that some sort of action takes places in the material containing fluorine that tends to expose groups that interact with the setting catalysts in the silicone-based resin at the surface, thus making the silicone-based resin more difficult to harden.
However, by interposing an intermediate layer between the cladding layer and the silicone-based resin, these interactions could be restricted, and the silicone-based resin could be properly set. In other words, by providing an intermediate layer, the inhibitions to the hardening of the silicone-based resin could be restricted even if the surface is cleaned as described above.
The intermediate layer can be formed from any material that is not a resin containing 10% fluorine or greater and that can assure adequate heat resistance for standard reliability tests for 2000 hours at 85 C, the maximum temperature. For example, metal films, dielectrics, or resin containing no fluorine or no more than 5% fluorine can be used, although the present invention is not restricted to these.
The resin layer containing no fluorine or no more than 5% total weight of fluorine can be any resin that can assure adequate beat resistance for standard reliability tests for 2000 hours at 85 C, the maximum temperature. For example, the material can be any of the following: thermosetting or ultraviolet-setting epoxy-based resin or acrylic-based resin; polyetherimide-based resin, polysulfone-based resin; polyethersulfone-based resin; polyvinylacetal-based resin; polyimide-based resin; polyimide-based resin; polyether ether ketone-based resin; a positive or negative photosensitive resist material or a base polymer of these; polyimide-based resin; or the like. Of these, polyimide-based materials provide wide production process margins since they generally have good chemical resistance properties. Also, since heat-resistance and climate-resistance properties are good, additional advantages such as good reliability can be provided.
These and other embodiments of the present invention are described in more detail in conjunction with the text below and attached figures.